The objective of this project is to understand the cellular mechanisms of the maternal/fetal transfer of important nutrients by the placenta. The proposed Aims involve 1) the cloning of the cDNAs for the trophoblast protein species mediating cationic amino acid transport; 2) the characterization of their functional capacities in an expression system to compare their activities with those of placental membranes; 3) the development and use of antibodies to the cloned transporter proteins for the quantitative assessment of transporter protein in microvillous and basal membranes, as well as other placental sources; and 4) the understanding of transporter regulation during trophoblast differentiation and membrane specialization.